1. Field of the Invention
The present general inventive concept relates to an image forming apparatus which transfers and superimposes individual color developer images onto a transfer unit, thereby realizing a color image, and a control method thereof.
2. Description of the Related Art
In general, an image forming apparatus, such as a printer, photocopier, facsimile, and multifunction peripheral which incorporates several functions in one device, forms an input image on a printing medium.
Such an image forming apparatus includes a photoconductive medium on which an electrostatic latent image is formed, a developing unit to develop the electrostatic latent image with a developer, a transfer unit to transfer the developed image to a printing medium, a fusing unit to fuse the transferred image onto the printing medium, and a discharge unit to discharge the printing medium to the outside.
Referring to FIG. 1, in order to realize a color image, first through fourth photoconductive media 1, 2, 3, 4 and first through fourth developing units 5, 6, 7, 8 are provided. Color electrostatic latent images are respectively formed on the first through fourth photoconductive media 1, 2, 3, 4, and these color electrostatic latent images are respectively developed into color developer images by the first through fourth developing units 5, 6, 7, 8. These color developer images developed on the first through fourth photoconductive media 1, 2, 3, 4 are transferred and superimposed onto a transfer unit 9 in sequence.
Developers moves from the first through fourth developing units 5, 6, 7, 8 to the first through fourth photoconductive media 1, 2, 3, 4 and then to the transfer unit 9 due to the existence of an electric potential difference.
However, a constant voltage is applied to the photoconductive media 1, 2, 3, 4, the developing units 5, 6, 7, 8, and the transfer unit 9. Also, as the developer images are transferred and superimposed from the first through fourth photoconductive media 1, 2, 3, 4 onto the transfer unit 9, an amount of developer to be transferred increases. However, the developers move between the first through fourth photoconductive media 1, 2, 3, 4 and the transfer unit 9 with the same electric potential difference. As a result, a transferring force does not correspond to the increased amount of developer, which deteriorates transfer quality.